Fire resistant polymeric compositions

ABSTRACT

A fire resistant composition for forming a fire resistant ceramic at elevated temperatures, the composition comprising: at least 15% by weight based on the total weight of the composition of a polymer base composition comprising at least 50% by weight of an organic polymer; and at least 20% by weight based on the total weight of the composition of a silicate mineral filler; wherein upon exposure to an elevated temperature (experienced under fire conditions), the fire resistant composition is useful for passive fire protection applications, particularly cables, the fluxing oxide is present in an amount of from 1 to 15% by weight of the residue.

FIELD OF THE INVENTION

The present invention relates to polymeric compositions which haveuseful fire resistant properties and which may be used in a variety ofapplications. The invention also relates to the preparation of suchcompositions and to their use. The present invention is illustrated withparticular reference to electric cables, although it will be appreciatedthat the invention is more widely useful in the light of the associatedbenefits described herein.

BACKGROUND

Passive fire protection of structures and components is an area that isreceiving increased attention. In this context the term “passive” meansthe use of materials that impart fire resistance. Passive fireprotection systems are used extensively throughout the building andtransportation industries and typically function by counteracting themovement of heat and/or smoke, by sealing holes, by prolonging stabilityof structures to which the system is applied and/or by creating thermaland/or physical barriers to the passage of fire, heat and smoke.

For many applications it is desirable that a material used to impartfire-resistance exhibits limited, and preferably no, substantial changein shape following exposure to the highest temperatures likely to beencountered in a fire situation (generally about 1000° C.). If thematerial shrinks significantly, its integrity is likely to becompromised and it may also crack and/or fracture. In turn this can leadto a breakdown in thermal and electrical insulation and a loss of firebarrier properties and fire resistance. As will be apparent from thefollowing, for many fire resistant polymeric compositions their inherentshrinkage on exposure to elevated temperature is an accepted consequenceof use. Specific measures taken to address this problem include theaddition of intumescing agents, which cause expansion but provide a verymechanically weakened residue, or engineering design solutions which addto the cost of the final product or structure.

Electric cables applications typically consist of a central conductorsurrounded by at least an insulating layer. Such cables find widespreaduse in buildings and indeed form the basis for almost all electriccircuits in domestic, office and industrial buildings. In someapplications, e.g. in emergency power supply circuits, there is arequirement for cables that continue to operate and provide circuitintegrity even when subjected to fire, and there is a wide range ofstandards for cables of this type. To meet some of these standards,cables are typically required to at least maintain electrical circuitintegrity when heated to a specified temperature (e.g. 650, 750, 950,1050° C.) in a prescribed manner and for a specified time (e.g. 15 min.,30 min., 60 min., 2 hours). In some cases the cables are subjected toregular mechanical shocks during the heating stage. For example, theymay be subjected to a water jet or spray either in the later stages ofthe heating cycle or after the heating stage. To meet a given standard acable is typically required to maintain circuit integrity throughout thetest. Thus it is important that the insulation maintains lowconductivity (even after prolonged heating at high temperatures),maintains its shape so it does not shrink and crack, and is mechanicallystrong, particularly if it is required to remain in place during shocksuch as that resulting from mechanical impact due to water jet or sprayexposure. It is also desirable that the insulation layer remaining afterheating resists the ingress of water if the cable is required tocontinue operating during exposure to water spray for brief periods.

One method of improving the high temperature performance of an insulatedcable has been to wrap the conductor of the cable with tape made withglass fibres and coated with mica. Such tapes are wrapped around theconductor during production and then at least one insulative layer isapplied. Upon being exposed to increasing temperatures, the outerlayer(s) are degraded and fall away, but the glass fibres hold the micain place. These tapes have been found to be effective for maintainingcircuit integrity in fires, but are quite expensive. Further, theprocess of wrapping the tape around the conductor is relatively slowcompared with other cable production steps, and thus wrapping the tapeslows overall production of the cable, again adding to the cost. A fireresistant coating that could be applied during the production of thecable by extrusion, thereby avoiding the use of tapes, would bedesirable.

A variety of materials have been used to impart fire resistance tostructures and components, including electric cables. The use ofcompositions based on silicone elastomers has been widespread. However,silicone elastomers can be expensive, have relatively poor mechanicalproperties and can be difficult to process, for example by extrusiontechniques. Furthermore, these compositions tend to have the associateddisadvantage that they are converted to powdery substances when exposedto fire because the organic components of the silicone elastomers arepyrolised or combusted. The pyrolysis or combustion products arevolatilised and leave an inorganic residue or ash (silicon dioxide) thathas little inherent strength. This residue is generally not coherent orself-supporting and indeed is often easily broken, dislodged orcollapsed. This behaviour mitigates against using silicone elastomers aspassive fire protection elements. This means, for instance, thatsilicone polymers used as insulation on electric cables must beprotected and held in place with physical supports such as inorganictapes and braids or metal jackets. On exposure to elevated temperatures,compositions in accordance with the present invention may form aphysically strong coherent layer around an electrical conductor andtherefore do away with the need to use such physical supports.

Certain compositions that exhibit fire-resistance do not also displaysuitably high electrical resistivity at elevated temperature. When usedin cable applications these compositions provide only thermal insulationand/or a physical barrier between the conductor and supporting metaltrays or brackets and tend to be electrically conducting in a firesituation leading to circuit failure. In this case additional steps mustbe taken to ensure electrical insulation is maintained at elevatedtemperature. For instance, a composition which imparts thermalresistance and/or provides a physical barrier at elevated temperaturebut which becomes electrically conducting may be provided over aseparate layer specifically incorporated in the design to provideelectrical insulation. It would be desirable to provide a singlecomposition which confers the required thermal insulation and/orprovides the required self-supporting and coherent physical barrier (egno cracking or fracturing) at elevated temperatures. Furthermore, it isalso desirable that this composition functions as an electricalinsulator at those temperatures. This is likely to provide significantcost savings and simplify product manufacture.

A further property often required of fire-resistant compositions is thatthey do not yield any potentially toxic gases or residues when exposedto a fire. Compositions of the present invention may also be inherentlysafe in this respect.

SUMMARY OF THE INVENTION

The present invention seeks to provide fire-resistant compositions whichexhibit limited, and preferably no, shrinkage when exposed to the kindof elevated temperatures associated with a fire. Furthermore, at suchtemperatures the compositions may also yield residue which isself-supporting (ie they remain rigid and do not undergo heat induceddeformation or flow) and coherent and has good mechanical strength, evenafter cooling. The residue is retained in its intended position ratherthan fracturing and being displaced, for example, by mechanical shock.In this context the term ‘residue’ is hereinafter intended to describethe product formed when the composition is exposed to an elevatedtemperature, experienced under fire conditions. These conditions aresimulated in this invention by slowly heating the fire resistantcompositions to 1000° C. and maintaining them at this temperature for 30minutes. Desirably, as well as providing thermal insulation and/or acoherent physical barrier or coating, compositions in accordance withthe present invention may also exhibit the required electricalinsulating properties at elevated temperatures.

Compositions in accordance with the present invention may also haveexcellent processability enabling them to be manufactured and used withease by conventional techniques. In addition the invention allows thepreparation of fire resistant polymer products with a wide range ofmechanical properties so that the invention can be tailored to suit therequirements of many different applications.

In general terms, the present invention provides a fire resistantcomposition which comprises inorganic components dispersed in a polymerbase composition comprising an organic polymer. The composition isconverted into a solid ceramic material after exposure to elevatedtemperature. In this context a ceramic is an inorganic non-metallicsolid material prepared by high temperature processing (e.g. above about400° C.). The invention seeks to provide fire resistant compositionswhich undergo limited or no substantial change in dimension and areself-supporting when exposed to fire and which are capable of providinga residual coating that has coherence and adequate physical properties.Such compositions would have widespread application in providing fireresistance to structures and components thereof. The compositions areparticularly useful for providing fire resistant insulation forelectrical cables as they may provide suitably high electricalresistivity and breakdown strength, even after prolonged heating at hightemperature. They can also provide circuit integrity when subsequentlysubjected to water spray. Use of a polymer base composition comprisingan organic polymer affords the potential for cost savings, enhancedprocessability and improved mechanical properties when compared withsystems where the polymer base composition is a silicone polymer.

Accordingly, in one aspect, the present invention provides a fireresistant composition for forming a fire resistant ceramic at elevatedtemperatures, the composition comprising:

-   -   at least 15% by weight based on the total weight of the        composition of a polymer base composition comprising at least        50% by weight of an organic polymer;    -   at least 15% by weight based on the total weight of the        composition of a silicate mineral filler; and    -   at least one source of fluxing oxide which is optionally present        in said silicate mineral filler,    -   wherein after exposure to an elevated temperature experienced        under fire conditions, a fluxing oxide is present in an amount        of from 1 to 15% by weight of the residue.

The fluxing oxide may be derived from the silicate mineral filler and/orone or more added fluxing oxide or fluxing oxide precursor.

In another aspect of the invention, there is provided a fire resistantcable formed from the fire resistant composition. According to thisaspect, there is provided a fire resistant cable comprising a conductiveelement and at least one insulating layer and/or sheathing for providinga fire resistant ceramic under fire conditions, the insulating layerand/or sheathing layer comprising:

-   -   at least 15% by weight based on the total weight of the        composition of a polymer base composition comprising at least        50% by weight of an organic polymer;    -   at least 15% by weight based on the total weight of the        composition of a silicate mineral filler; and    -   at least one source of fluxing oxide which is optionally present        in said silicate mineral filler,    -   wherein after exposure to an elevated temperature experienced        under fire conditions, a fluxing oxide is present in an amount        from 1 to 15% by weight of the residue.

The fluxing oxide may be derived from the silicate mineral filler and/orone or more separately added fluxing oxide or fluxing oxide precursors.

It has been found that compositions in accordance with the presentinvention may form a coherent ceramic product when exposed to elevatedtemperatures and that this product exhibits desirable physical andmechanical properties. The ceramic char formed after exposure ofcompositions of the present invention at an elevated temperature not inexcess of 1050° C. preferably has a flexural strength of at least 0.3MPa. It is a distinct advantage that the compositions are selfsupporting, i.e. they remain rigid and do not undergo heat induceddeformation or flow. They also undergo little if any shrinkage followinghigh temperature exposure, whether the heating rate experienced isrelatively fast or slow. Typically rectangular test specimens exposed tothe prescribed slow firing conditions used in this invention willundergo changes in linear dimension along the length of the specimen ofless than 10%, preferably less than 5% and most preferably less than 1%.Changes in dimension are also influenced by additional factors includingthe thermal degradation behaviour of the polymeric component, and canvary from shrinkage to expansion (caused by gases escaping fromdecomposing components of the composition), with expansion having themost pronounced effect (in a percentage change basis) in the leastconstrained dimension such as the thickness (height) of a rectangularsheet shape specimen. Thus one skilled in the art can select thecomponents of the composition to achieve a range of outcomes under theexpected heating conditions, for example: no significant change inlinear dimension, net shape retention, an increase in linear dimensionof under 5%, etc.

It is a further advantage, of the compositions of the present invention,that this type of coherent product with desirable physical andmechanical properties can be formed at temperatures well below 1000° C.The compositions of the invention may be used in a variety ofapplications where it is desired to impart fire resistance to astructure or component. The compositions are therefore useful in passivefire protection systems.

In a preferred form of the invention after firing, the fluxing oxide ispresent in an amount of 2-10% by weight of the residue and the weight ofthe residue is at least 40% of the weight of the fire resistantcomposition. Hence firing results in a weight reduction of less than60%.

The applicants have found that compositions having fluxing oxide levelsin the residue of greater than 15% by weight, experience sustainedchanges in linear dimension caused by shrinkage when subjected toelevated temperatures which can be experienced under fire conditions.For fire protection applications, it is preferable that this change inlinear dimension is less than 10% and more preferably less than 5%, andmost preferably less than 1%. Hence, the amount of fluxing oxide in theresidue is adjusted to ensure that the composition or articles formedfrom the composition comply with the desired linear dimension changelimits for a given application at the fire rating temperature. Asmentioned earlier, the standards for fire rating of cables varydepending on the country, but are generally based on heating the cablesto temperatures such as 650°, 750°, 950°, 1050° in a prescribed mannerfor a specified time such as 15 minutes, 30 minutes, 60 minutes and 2hours.

As the composition is required to form a self-supporting porous ceramic(typically having porosity of between 20 vol % to 80 vol %) when exposedto fire rating temperatures, it is essential that the composition doesnot fuse. In the context of this invention, fuse means that the liquidphase produced in the composition becomes a continuous phase, and/orthat the reacting mineral silicate fillers particles (eg mica) largelylose their original morphology, and/or that the amount of liquid phaseproduced becomes sufficient to cause the ceramic to deform due to itsown weight. The upper limit for the fluxing oxide content of the residueis 15% by weight to avoid fusing of the composition occurring below theupper temperature of the exposure. Thus in the resulting ceramic thereacting mineral silicate particles (eg mica particles) essentiallyretain their morphology, with only minor changes at the edges as aresult of ‘bridging’ to other particles.

The composition of the present invention includes as an essentialcomponent an organic polymer. An organic polymer is one which has anorganic polymer as the main chain of the polymer. For example, siliconepolymers are not considered to be organic polymers; however, they may beusefully blended with the organic polymer(s), as the minor component,and beneficially provide a source of silicon dioxide (which assists information of the ceramic) with a fine particle size when they arethermally decomposed. The organic polymer can be of any type, forexample a thermoplastic polymer, a thermoplastic elastomer, acrosslinked elastomer or rubber, a thermoset polymer. The organicpolymer may be present in the form of a precursor composition includingreagents, prepolymers and/or oligonomers which can be reacted togetherto form at least one organic polymer of the types mentioned above.

The organic polymer component can comprise a mixture or blend of two ormore different organic polymers.

Preferably, the organic polymer can accommodate high levels of inorganicadditives, such as the silicate mineral filler, whilst retaining goodprocessing and mechanical properties. It is desirable in accordance withthe present invention to include in the fire resistant compositions highlevels of inorganic filler as such compositions tend to suffer reducedweight loss on exposure to fire when compared with compositions havinglower filler content. Compositions loaded with relatively highconcentrations of silicate mineral filler are therefore less likely toshrink and crack when ceramified by the action of heat. The presence inthe compositions of the invention of the specified range of fluxingoxide is also believed to contribute in this respect.

It is also advantageous for the chosen organic polymer not to flow ormelt prior to its decomposition when exposed to the elevatedtemperatures encountered in a fire situation. The most preferredpolymers include ones that are cross-linked after the fire resistantcomposition has been formed, or ones that are thermoplastic but havehigh melting points and/or decompose to form a char near their meltingpoints; however, polymers that do not have these properties may also beused. Suitable organic polymers are commercially available or may bemade by the application or adaptation of known techniques. Examples ofsuitable organic polymers that may be used are given below but it willbe appreciated that the selection of a particular organic polymer willalso be impacted by such things as the additional components to beincluded in the fire resistant composition, the way in which thecomposition is to be prepared and applied, and the intended use of thecomposition.

As indicated, organic polymers that are suitable for use with thisinvention include thermoplastic polymers, thermoset polymers, and(thermoplastic) elastomers. Such polymers may comprise homopolymers andcopolymers of polyolefins, vinyl polymers, acrylic and methacrylicpolymers, styrene polymers, polyamides, polyimides, epoxides,polyoxymethylene acetals, polycarbonates, polyurethanes, polyesters,phenolic resins and melamine-formaldehyde resins.

By way of illustration, examples of thermoplastic polymers suitable foruse include polyolefins, polyacrylates, polycarbonates, polyamides(including nylons), polyesters, polystyrenes, polyurethanes and vinylpolymers. Suitable vinyl polymers include poly(vinyl chloride) (PVC) andpoly(vinyl acetate) (PVAc).

Suitable polyolefins include homopolymers or copolymers, of alkylenes.Specific examples of suitable polyalkylenes include polymers of thefollowing olefins: ethylene, propylene, butene-1, isobutylene,hexene-1,4-methylpentene, pentene-1, octene-1, nonene-1 and decene-1.These polyolefins may be prepared using peroxide, organometalliccomplexing catalysts, Ziegler-Natta or metallocene catalysts, as is wellknown in the art. Copolymers of two or more of these olefins may also beemployed, for example, ethylene-propylene copolymers and terpolymers(eg. EPDM), ethylene-butene-1 copolymers, ethylene-hexene-1 copolymers,ethylene-octene-1 copolymers and other copolymers of ethylene with oneor more of the above-mentioned olefins. The olefins may also becopolymerised with other monomer species such as vinyl, acrylic or dienecompounds. Specific examples of suitable ethylene-based copolymersinclude ethylene-vinyl acetate (EVA), ethylene-alkyl acrylate,preferably ethylene-ethyl acrylate (EEA) or ethylene-butyl acrylate(EBA), and ethylene-fluoroolefinic monomers, for example,ethylene-tetrafluoroethylene (ETFE).

The thermoplastic polyolefin may also be a blend of two or more of theabove-mentioned homopolymers or copolymers. For example, the blend canbe a uniform mixture of one of the above systems with one or more ofpolypropylene, polybutene-1 and polar monomer-containing olefincopolymers. Preferably, the polar-monomer containing olefin copolymerscomprises ethylene with one or more of acrylic or vinyl monomers, suchas ethylene-acrylic acid copolymers, ethylene-alkyl acrylate copolymers,preferably, ethylene-methyl acrylate, ethylene-ethyl acrylate orethylene-butyl acrylate copolymers, ethylene-vinyl copolymers,preferably ethylene-vinyl acetate and ethylene-acrylic acid/ethylacrylate and ethylene-acrylic acid-vinyl acetate terpolymers.

Suitable elastomers may comprise a variety of rubber compositions, suchas natural rubber (NR), butyl rubber (IIR), styrene-butadiene rubber(SBR), nitrile-butadiene rubber (NBR), ethylene-propylene rubber (EPM),ethylene-propylene terpolymer rubber (EPDM), epichlorohydrin rubber(ECH) polychloroprene (CR), chlorosulfonated polyethylene (CSM) andchlorinate polyethylene (CM). Suitable thermoplastic elastomers mayinclude styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS)and styrene-ethylene-butadiene-styrene (SEBS).

Suitable thermoset polymers may comprise phenolic resins,melamine-formaldehyde resins, urethane resins, acrylic resins, epoxyresins, polyester resins and vinyl ester resins. Thermoset resins may beproduced by any method as is well known in the art.

The organic polymers may be fabricated in the composition by any numberof means, including but not limited to in situ polymerisation ofmonomers, prepolymers or reactive starting compounds and crosslinking orcuring of suitable reactive intermediates. Specific examples of suitablemonomers, prepolymers and reactive compounds include acrylates,urethanes, epoxides, vinyl esters, phenol, formaldehyde, anhydrides andamines. Curing additives may also be added to assist in generation ofthe thermoset polymer.

The organic polymer may also be dissolved in a suitable solvent or be ina dispersed form in water or prepared as an emulsion or dispersion inwater in order to generate suitable compositions. The emulsion may alsobe a water-in-oil type. There is wide range of organic polymers andcopolymers that can be obtained commercially as water-based dispersionsor emulsions that can be used in this invention, for example: acrylics,polyurethanes, EVAs, vinyl esters polymers including poly(vinylacetate), SBRs.

Coatings and sealants based on organic polymers may be prepared by anumber of means, including the use of solvents, emulsions ordispersions. For example, the composition of the present invention maybe dissolved or dispersed in water or a suitable solvent, then applied.After application, the mixture may be dried and any solvent evaporated.Where the polymer is a thermoset polymer, the drying step may assist incuring of the reactive intermediates together with any curing additivesto form the required coating or sealant.

The organic polymers that are particularly well suited for use in makingcoatings for cables are commercially available thermoplastic andcrosslinked olefin based polymers, co- and terpolymers of any density.Co monomers of interest will be well known to those skilled in the art.Of particular interest are commercially available thermoplastic andcrosslinked polyethylenes with densities from 890 to 960 kg/litre,copolymers of ethylenes of this class with acrylic, vinyl and otherolefin monomers, terpolymers of ethylene, propylene and diene monomers,so-called thermoplastic vulcanisates where one component is crosslinkedwhile the continuous phase is thermoplastic and variants of this whereall of the polymers are either thermoplastic or crosslinked by eitherperoxide, radiation or so-called silane processes.

Compositions of the invention may be formed about a conducting elementor plurality of elements by extrusion (including co-extrusion with othercomponents) or by application of one or more coatings.

As noted, the organic polymer chosen will in part depend upon theintended use of the composition. For instance, in certain applications adegree of flexibility is required of the composition (such as inelectrical cable coatings) and the organic polymer will need to bechosen accordingly based on its properties when loaded with additives.Also in selecting the organic polymer account should be taken of anynoxious or toxic gases which may be produced on decomposition of thepolymer. The generation of such gases may be more tolerable in certainapplications than others. Preferably, the organic polymer used ishalogen-free.

The polymer base composition can also include at least one other polymerwhich is not an organic polymer.

Thus, compositions of the present invention may also include a siliconepolymer in combination with the organic polymer as the polymer basecomposition in which the additional components are dispersed.

When used, the nature of the silicone polymer is not especially criticaland one skilled in the art will be aware as to the type of polymerswhich may be used, although account should be had for the various issuesdescribed above in connection with the organic polymer (compatibilityetc.). Useful silicone polymers are described in detail in the prior artincluding U.S. Pat. No. 4,184,995, U.S. Pat. No. 4,269,753, U.S. Pat.No. 4,269,757 and U.S. Pat. No. 6,387,518. By way of more specificillustration, the silicone polymer may be an organopolysiloxane composedof units of formula: $R_{r}\text{SiO}_{\frac{4 - r}{2}}$in which

R may be identical or different and are unsubstituted or substitutedhydrocarbon radicals, r is 1, 2, 3 or 4 and has an average numericalvalue of from 1.9 to 2.1.

Examples of hydrocarbon radicals R are alkyl radicals, such as themethyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl,n-pentyl, isopentyl, neopentyl, tert-pentyl and hexyl radicals, such asn-hexyl, heptyl radicals, such as the n-heptyl, octyl radicals, such asthe n-octyl, and isooctyl radicals, such as the 2,2,4-trimethylpentyl,nonyl radicals, such as the n-nonyl, decyl radicals, such as then-decyl, dodecyl radicals, such as the n-dodecyl, octadecyl radicals,such as the n-octadecyl; cycloalkyl radicals, such as cyclopentyl,cyclohexyl and cycolheptyl and methyl cyclohexyl radicals; arylradicals, such as the phenyl, biphenyl, napthyl and anthryl andphenanthryl; alkaryl radicals, such as o-, m- or p-tolyl radicals, xylyland ethylphenyl radicals; and aralkyl radicals, such as benzyl and α-and β-phenylethyl.

Examples of substituted hydrocarbon radicals R are halogenated alkylradicals, such as 3-chloropropyl, the 3,3,3-trifluoropropyl and theperfluorohexylethyl and halogenated aryl, such as the p-chlorophenyl andthe p-chlorobenzyl.

The radicals R are preferably hydrogen atoms or hydrocarbon radicalshaving from 1 to 8 carbon atoms, preferably methyl. Other examples ofradicals R are vinyl, allyl, methallyl, 1-propenyl, 1-butenyl and1-pentenyl, and 5-hexenyl, butadienyl, hexadienyl, cyclopentenyl,cyclopentadienyl, cyclohexenyl, ethynyl, propargyl and 1-propynyl. Theradicals R are preferably alkenyl radicals having from 2 to 8 carbonatoms, particularly vinyl.

The end groups of the polymers may be trialkylsiloxy groups, for exampletrimethylsiloxy or dimethylvinylsiloxy groups, or derived groups whereone or more of the alkyl groups has been replaced by hydroxy or alkoxygroups.

The silicone polymer may be crosslinkable. The crosslinkable polymer canbe any one which can be crosslinked by any one of the methods used forcommercially available organopolysiloxane polymers including by freeradical crosslinking with a peroxide through the formation of ethylenicbridges between chains, by addition reactions including reaction ofsilylhydride groups with allyl or vinyl groups attached to silicon,through condensation reactions including the reactions of silanols toyield Si—O—Si crosslinks, or using other reactive groups. Depending onthe type of silicone polymer used the composition will therefore furthercomprise a suitable crosslinking agent. Suitable crosslinking agents arecommercially available, for example there is a wide range of usefulperoxides suitable for use in this application, such as dibenzoylperoxide, bis (2,4-dichlorobenzoyl) peroxide, dicumyl peroxide or2,5-bis(tert-butylporoxy)-2,5-dimethylhexene or also mixtures of these,and when appropriate they may be included in the composition during thecompounding process.

A silicone polymer type especially suitable for cable insulation iswhere the silicone polymer is of high molecular weight and has vinylside chains that require heat to crosslink, either through platinumcatalysed addition reactions or peroxide initiated free radicalreactions. These silicone polymers are widely available commerciallyfrom major silicone producers.

The organopolysiloxane materials may also comprise reinforcing fillerssuch as precipitated or pyrogenic silicas and/or non-reinforcingfillers. Further, the surface of these silica type fillers may bemodified by straight or branched organopolysiloxanes,organo-chlorosilanes and/or hexamethyl disilazanes.

The organic polymer is present in the polymer base composition in anamount of at least 50% by weight. This facilitates loading of thepolymer base composition with the additional components withoutdetriment to the processability of the overall composition. As noted thepolymer base composition may include a silicone polymer. However, inthis case the organic polymer would usually be present in the polymerbase composition in a significant excess when compared with the siliconepolymer. Thus, in the polymer base composition the weight ratio oforganic polymer to silicone polymer may be from 5:1 to 2:1, for instancefrom 4:1 to 3:1. In terms of weight percentage, if present, the siliconepolymer might generally be present in an amount of from 2 to 15% byweight based on the total weight of the formulated fire resistantcomposition. When a combination of organic and silicone polymers areused, high concentrations of silicone polymer can present processingproblems and this should be taken into account when formulatingcompositions in accordance with the present invention.

The upper limit for the amount of polymer base composition in the fireresistant composition tends to be influenced by the desired propertiesof the formulated composition. If the amount of the polymer basecomposition exceeds about 60% by weight of the overall composition, itis unlikely that a cohesive, strong residue will be formed during a firesituation. Thus, the polymer base composition generally forms from 10 to60%, preferably from 20 to 50%, by weight of the formulated fireresistant composition.

The compositions in accordance with the present invention also include asilicate mineral filler as an essential component. Such fillerstypically include alumino-silicates (e.g. kaolinite, montmorillonite,pyrophillite—commonly known as clays), alkali alumino-silicates (e.g.mica, felspar, spodumene, petalite), magnesium silicates (e.g. talc) andcalcium silicates (e.g. wollastonite). Mixtures of two or more differentsilicate mineral fillers may be used. Such fillers are commerciallyavailable. Silicon dioxide (silica) is not a silicate mineral filler inthe context of the present invention.

The silicate mineral filler may be surface treated with a silanecoupling agent in order to enhance its compatibility with othermaterials present in the compositions of the present invention.

The compositions of the invention include at least 15% by weight,preferably at least 25% by weight and more preferably at least 55% byweight, silicate mineral filler. The maximum amount of this componenttends to be dictated by the processability of the composition. Very highlevels of filler can make formation of a blended composition difficult.Usually, the maximum amount of silicate mineral filler would be about80% by weight. The amount and type of silicate mineral filler used willalso be dictated by the requirement to have a certain range of fluxingoxide in the residue formed by heating the composition at elevatedtemperatures experienced under fire conditions. As will be explained,the fluxing oxide can be generated in situ at elevated temperature byheating certain types of silicate mineral fillers (eg mica), to make thefluxing oxide become available at the surfaces of the filler particles.Additionally, or alternatively the fluxing oxide may come from a sourceother than the silicate mineral filler. As is explained later, thefluxing oxide is believed to act as an “adhesive” assisting in formationof a coherent product at high temperature. The fluxing oxide is believedto contribute a binding flux at the edges of the filler particles. Thepresence of a high proportion of silicate mineral filler results in acomposition which is likely to exhibit low shrinkage and cracking when aceramic is formed at elevated temperature, and on cooling of theceramic.

The compositions of the present invention also include a fluxing oxideas an essential component. By this it is meant an oxide that melts byitself below 1000° C. or reacts with a silicate or other inorganiccomponent to melt at temperatures below about 1000° C. The generation ofsuch a liquid phase, as well as the amount generated, play an importantrole in yielding a ceramic structure having a desirable combination ofproperties following exposure at elevated temperature. As noted, thefluxing oxide may be generated by heating certain silicate mineralparticles (eg mica) to make the fluxing oxide become available at thesurface of the particles. Alternatively, or additionally, a fluxingoxide or precursor thereof may be added to the composition.

Without wishing to be bound by theory, it is believed that compositionsin accordance with the present invention form a coherent ceramic productafter exposure to elevated temperatures as a result of a fluxing oxidelocally forming a eutectic composition at the interface of the silicatemineral filler particles and/or of other inorganic particles present inthe composition or formed from decomposition thereof. These inorganicparticles include other silicates minerals, and possibly silicon dioxide(either derived from heating the silicate mineral filler, added as anadditional filler and/or generated by thermal decomposition of asilicone polymer or any silicone additive). When the fluxing oxide isadded as a separate component to the composition, a eutectic forms atthe interface between the fluxing oxide and the contacting reactiveparticles. Ordinarily the silicate mineral filler, and any additionalinorganic components, each have very high melting points. However, thepresence of the fluxing oxide may result in eutectics at the interfacesof these causing melting at lower temperatures. The fluxing oxide causesformation of a eutectic which may act as a “bridge” between theparticles of silicate mineral filler and other inorganic componentspresent. This is thought to assist in “binding” the decompositionproducts of the composition, silicate mineral filler, and, when present,other components. In this way formation of a coherent ceramic product isimproved and it is possible to reduce the temperature required to form acomparatively strong porous ceramic material. It is very important tocontrol the extent of eutectic formation and melting in the compositionto control shrinkage and the creation of molten conductive pathways inthe heated material. Compositions in accordance with the presentinvention may yield a coherent porous ceramic product that isself-supporting and undergoes limited, and preferably no, shrinkagefollowing exposure to elevated temperature in a fire.

In general the fluxing oxide additive may be any compound which iscapable of functioning in the manner described in order to form aceramic product having the desired combination of properties. Inpractice, however, the fluxing oxide is likely to be boron oxide or ametal oxide selected from the oxides of lithium, potassium, sodium,phosphorus, and vanadium. As mentioned, the fluxing oxide may begenerated by heating certain silicate mineral fillers (eg mica), it canbe separately added or it is also possible to include in compositions ofthe present invention, a precursor of the fluxing oxide (eg a metalhydroxide or metal carbonate precursors to the metal oxides), that is acompound that yields the fluxing oxide following exposure at the kind ofelevated temperatures likely to be encountered in a fire. In that casethe fluxing oxide is likely to be formed by thermal decomposition of theprecursor. Similarly, when boric oxide is used as the fluxing oxide, itmay be derived from a suitable precursor compound. Borates, andparticularly zinc borate, provide useful precursors for boric oxide.

While lead oxide and antimony oxide can be used as fluxing oxides,usually the compositions of this invention are free from lead andantimony as they may constitute health and safety problems due to theirtoxicity.

The fluxing oxide precursor may be a glass and a variety of glasses maybe used. It should be noted however that to remain electricallyinsulating a low alkali metal content in the flux is desirable. Theglass may take a variety of forms such as powder or fibres. Mixtures ofone or more of these may be used. The preferred form is glass powder orfrit. Irrespective of form, the glass additive preferably has asoftening point below 1000° C., for example, below 800° C., and mostpreferably between 300 and 800° C. The softening point of the glass isdefined by the temperature at which the viscosity of the glass equal10^(7.6) poise. The glass additive may be one or a combination ofsilicate, borate and/or phosphate glass systems. Suitable glassadditives are commercially available.

As described, it is quite possible that one or more silicate mineralfiller will contribute fluxing oxide following exposure at elevatedtemperature. In one embodiment, all of the fluxing oxides are derivedfrom the silicate mineral filler(s). In another embodiment, the fluxingoxide is derived from the silicate mineral filler and another source,and this may lead to advantages in terms of the structure formed atelevated temperature due to fluxing oxide being provided from withinparticles of the silicate mineral filler and external to such particles.In a further embodiment the fluxing oxide is derived from the silicatemineral filler and an added boric oxide or a source of boric oxide (e.g.zinc borate). In a further embodiment the fluxing oxide is derived fromthe silicate mineral and added glass. In yet another embodiment fluxingoxide is derived from the silicate mineral added glass and boric oxideor a source of boric oxide. In a yet further embodiment the fluxingoxide is derived from a source or sources other than the silicatemineral filler.

In one embodiment the composition includes at least two differentfluxing oxides which form liquid phases at different temperatures. Thiscan enhance char integrity as well as ensuring that the compositionfunctions as required over a broad temperature range.

The compositions should be formulated so that the residue formedcontains 1-15%, and preferably 1-10%, more preferably 2-8% of a fluxingoxide regardless of the source of this oxide. In other words 15% byweight is the maximum amount of fluxing oxide that should be present inthe residue. When the fluxing oxide is derived from the silicate mineralfiller or precursor such as zinc borate or other additive, the amount offluxing oxide may be calculated on the basis of the maximum amount offluxing oxide this component would yield at elevated temperature. Thiscalculation will, for instance, be based on the total amount of elementssuch as boron, phosphorus, lithium, sodium, potassium and vanadium whichare present in the silicate mineral filler, borate and other additivesand which can in theory result in formation of the corresponding fluxingoxides. To minimise shrinkage, it is preferred that the amount offluxing oxide is as low as necessary to enable formation of a coherentceramic product on exposure to the kind of elevated temperatureencountered in a fire. It has also been found that the physical form ofthe filler can influence the extent of shrinkage when the composition isheated. More specifically, it has been found that fillers composed oflarge platelike particles confer less shrinkage and thus lowerpercentage changes in linear dimension.

Preferably, the compositions of the present invention include at leastone silicate mineral that is an appreciable source of fluxing oxide.Mica satisfies this requirement and provides additional benefits becauseit is also available in plate form, making it a preferred component. Thetwo most common classes of commercially available mica are muscovite andphlogopite, and these are therefore typically used in the presentinvention. Muscovite mica is a dioctahedral alkali aluminium silicate.Muscovite has a layered structure of aluminium silicate sheets weaklybonded together by layers of potassium ions. It has the followingcomposition KAl₃Si₃O₁₀(OH)₂. Phlogopite mica is a trioctahedral alkalialuminium silicate. Phlogopite has a layered structure of magnesiumaluminium silicate sheets weakly bonded together by layers of potassiumions. It has the following composition KMg₃A1Si₃O₁₀(OH)₂. Both micatypes are typically present in the form of thin plates or flakes havingsharply defined edges.

The composition of the present invention may contain silicon dioxide asa result of being exposed to elevated temperature. For instance, thissilicon dioxide may be derived from heating the silicate mineral filler.It may also come from thermal decomposition of a silicone polymer whenincluded in the polymer base composition. Silica may also be added as aseparate filler component.

In addition to the mineral silicate fillers, a wide variety of otherinorganic fillers may be added. Preferred inorganic fillers are silicondioxide and metal oxides of calcium, iron, magnesium, aluminium, zircon,zinc, tin and barium (preferably added as fine powders), or inorganicfillers which generate these oxides when they thermally decomposes (egthe corresponding carbonates and hydroxides), since these oxides canreact and/or sinter at less than 1000° C. the other inorganic componentsto assist in formation of the self supporting ceramic.

Also inorganic fibres which do not melt at 1000° C. can be incorporated,including aluminosilicate fibres. This may lead to a reduction indimensional changes at elevated temperature and/or improved mechanicalproperties of the resulting ceramic.

Usually, after exposure at elevated temperature (to 1000° C.) theresidue remaining will generally constitute at least 40%, preferably atleast 55% and more preferably at least 70%, by weight of the compositionbefore pyrolysis. Higher amounts of residue are preferred as this mayimprove the char (ceramic) strength at all temperatures by bettermechanical interlocking of particles and also a reduced tendency toshrink.

As mentioned, it has also been found that the mechanical properties ofthe ceramic formed from the composition of the present invention can beenhanced by including in the composition a low level of boric oxide orprecursor thereof which yields boric oxide at elevated temperature e.g.zinc borate. In this case however the total amount of boric oxide andother fluxing oxides will not exceed 15% by weight of the residueobtained after heating the composition for 30 minutes at 1000° C.

It has also been found that removing volatile decomposition productsfrom fillers such as clay by calcining prior to addition to thecomposition reduces shrinkage when the composition of the invention isheated at an elevated temperature. This is believed to help reduce masschange and linear dimensional change of the composition when exposed toelevated temperature.

As explained, preferably the compositions exhibit minimal lineardimensional change after exposure to the kind of temperatures likely tobe encountered in a fire. By this is meant that the maximum lineardimensional change in a product formed from a composition in accordancewith the present invention is less than 10%, preferably less than 5% andmost preferably less than 1%. In some cases net shape retention is themost preferred property.

Compositions in accordance with the invention may also exhibit theelectrical insulating properties at high temperature that are requiredfor use in electric cables. Essentially this means that the electricalresistance of the material, while less than at room temperature, doesnot fall to a point where the normal operating voltage can overcome theinsulation resistance of the material and cause a short circuit.

The compositions of the invention are also preferably free of otherelements that may constitute a health and safety problem due totoxicity. Thus, the compositions are preferably free of halogencompounds.

For cable applications, where the electrical resistivity of thecomposition is important, the levels of alkali ions present must becarefully considered as they can cause electrical conductivity at hightemperatures. For example in a given composition, if the level of micais too high electrical integrity problems arise due to an unacceptablereduction in electrical resistivity of the composition and/or fromdielectric breakdown when the compositions are subjected to hightemperatures for an extended period of time. At high temperatures alkalimetal ions, for instance from mica, tend to provide conductive pathways,resulting in the need to limit the level of mica.

In a preferred form, the composition comprises a fire resistantcomposition according to claim 1, wherein:

-   -   20 to 75% by weight of said polymer base composition wherein        said composition further comprises a silicone polymer;    -   at least 15% by weight of an inorganic filler wherein said        inorganic filler comprises mica and a glass additive; and    -   wherein the fluxing oxide in the residue is derived from glass        and mica wherein, the ratio of mica:glass is in the range of        from 20:1 to 2:1. The organic filler may comprise 10 to 30% by        weight of the total composition of mica and 20 to 40% by weight        of the total composition of an additional inorganic filler.

In one embodiment of the present invention it has been found that havinga relatively high concentration of fluxing oxides in the composition ofthe invention can lead to formation of a glassy surface layer when thecomposition is ceramified (at elevated temperature) and cooled.Desirably, this surface layer has been found to confer improved waterresistance to the ceramic formed. The surface layer can also make theresulting ceramic a more effective barrier to the passage of gases andsmoke. The formation of such a surface layer, and associated enhancedwater resistance, is particularly beneficial in electrical cableapplications because ingress of water (used to quench a fire) throughthe ceramic is likely to lead to electrical shorting. Of course, thepotentially detrimental effects of high levels of a glass phase(shrinkage and electrical conductivity) must be taken into account. Theamount of fluxing oxide required to form the glassy surface layer whenthe composition forms a ceramic may vary depending upon the layerthickness (see below) and other ingredients present in the composition.However, in general terms the fluxing oxide level is desirably more than5% of the residue obtained after heating the composition for 30 minutesat 1000° C. The total amount of glass phase present in the heatedcomposition may be derived from a single source or from more than onesource. For instance, the glass phase may be derived predominantly fromglass frits, fibres and/or particles of the same or different typeglass. A similar effect may be observed by using a relatively highconcentration of mica, for example about 25% by weight, since this toocan lead to the formation of sufficient liquid phase during heating.

The mechanism by which the glassy surface layer (skin) is formed is notclearly understood, although glass flow is clearly required in order toform the (densified) glassy surface layer. This means that the meltingtemperature of the glass additive and/or the liquid phase formed byfluxing oxides from other sources must be selected so that some flow ispossible at the ceramic-forming temperature. It may be desirable toincorporate a variety of glass phases with different melting points toachieve skin formation and the desirable mechanical properties. Themechanism for formation of the glassy surface layer may be associatedwith surface tension effects between the molten glass and its localenvironment. One possible explanation for migration and aggregation ofglass to the surface of the formed ceramic is that the surface energy atthe glass/atmosphere interface is lower than that of the energy at theinterface between the molten glass and the bulk of the composition. Thisbeing so, the molten glass migrates to the lower energy interface.

It has been found that the thickness of the composition may have animpact on the formation of the water resistant surface layer. This isbelieved to be due to volume effects, with more glass (and/or mica)being available for formation of a suitably thick surface layer when thethickness of the composition is greater. It has been observed in factthat a thicker sample of a composition yields a more water resistantsurface layer than a thinner sample of the same composition.

Water resistance can also be improved by the addition of inorganicfibres which do not melt at 1000° C. Alumino-silicate fibres arepreferred and can be used at levels of up to 10% by weight.

Other components may be incorporated into the compositions of thepresent invention. These other components include lubricants,plasticisers, inert fillers (eg fillers that are not the metal oxidesthat can react and/or sinter with the other inorganic components, ortheir precursors), antioxidants, fire retardant materials, fibrereinforcing materials, materials that reduce thermal conductivity (egexfoliated vermiculite), chemical foaming agents (which serve to reducedensity, improve thermal characteristics and further enhance noiseattenuation), and intumescing materials (to obtain a composition thatexpands upon exposure to fire or elevated temperature). Suitableintumescing materials include natural graphite, unexpanded vermiculiteor unexpanded perlite. Other types of intumescing precursors may also beused. The total amount of such additional components does not usuallyexceed 20% by weight based on the total weight of the composition.

The composition containing an organic polymer can be prepared in anyconceivable way. This includes adding the other components to: a monomer(or mixture of monomers) which is (are) then polymerised; prepolymersand/or oligomers which are then polymerised by chain extension and/orcrosslinking reactions; thermoplastic polymers by melt blending; aqueousorganic polymer dispersions by dispersive mixing (where the waterpresent is not considered part of the composition in this invention); asolution of a polymer dissolved in a solvent (where the solvent presentis not considered part of the composition in this invention); andthermosetting systems which are subsequently crosslinked. Regardless howthe composition is prepared it is necessary that added components(mineral fillers, other inorganic components, and other organicadditives) can be effectively mixed with the organic polymer(s), or theprecursors used to form the polymer(s), so that they are well dispersedin the resulting composition and that the composition can be readilyprocessed to produce the desired end product.

Any conventional compounding equipment may also be used. If thecomposition has relatively low viscosity, it may be processed usingdispersing equipment, for instance of the type used in the paintindustry. Materials useful for cable insulation applications are ofhigher viscosity (higher molecular weight) and may be processed using atwo roll mill, internal mixers, twin-screw extruders and the like.Depending upon the type of crosslinking agent/catalyst added, thecomposition can be cured by exposure to air at 200° C., in an autoclavewith high pressure steam, using continuous vulcanisation equipmentincluding a liquid salt bath and, conceivably, by exposure to any mediumthat will cause the peroxide to decompose, including microwaves,ultrasonics etc.

The compositions of the present invention may be used in a large numberof applications where fire resistance is desired. For example, thecompositions may be used to form a fire resistant building panel or inthe manufacture of glass fibre reinforced polymer composites. Thecomposition may be used by itself or together with one or more layers ofother materials.

The compositions of the present invention may be provided in a varietyof different forms, including:

-   -   1. As a sheet, profile or complex shape. The composition may be        fabricated into these products using standard polymer processing        operations, eg extrusion, moulding (including hot pressing and        injection moulding). The products formed can be used in passive        fire protection systems. The composition can be used in its own        right, or as a laminate or composite with another material (for        example, plywood, vermiculite board or other). In one        application the composition may be extruded into shapes to make        seals for fire doors. In the event of a fire, the composition is        converted into a ceramic thus forming an effective mechanical        seal against the spread of fire and smoke.    -   2. As a pre-expanded sheet or profile. This form has additional        benefits compared with the above, including reduced weight and        the capacity for greater noise attenuation and insulation during        normal operating conditions. Porosity can be incorporated into        the material during manufacture of the sheet or profile by        thermal degradation of a chemical blowing agent to produce a gas        product, or by physically injecting gas into the composition        during processing before curing.    -   3. As an intumescent product, which expands by foaming when        exposed to heat or fire. In this application the product can be        used, for example, around pipework or penetrations between        walls. In the event of a fire the product expands to fill the        void and provide an effective plug to prevent the spread of        fire. The intumescent material may be in the form of an        extrudable paste or a flexible seal.    -   4. As a mastic material which can be applied (for example from a        tube as per a conventional silicone sealant) as a seal for        windows and other articles.    -   5. As a paint, or an aerosol based material, that could be        sprayed or applied by with a brush.

Specific examples of passive fire protection applications where thisinvention may be applied include but are not limited to firewall liningsfor ferries, trains and other vehicles, fire partitions, screens,ceilings and linings, structural fire protection [to insulate thestructural metal frame of a building to allow it to maintain itsrequired load bearing strength (or limit the core temperature) for afixed period of time], fire door inserts, window and door seals,intumescent seals, and compounds for use in electrical boxes, infittings, straps, trays etc that are attached to or used to house cablesor similar applications.

Another area of application is in general engineering. Specific areas ofgeneral engineering, where passive fire protection properties arerequired, include transportation (automotive, aerospace, shipping),defence and machinery. Components in these applications may be totallyor partially subject to fire.

When totally subject to fire, the material will transform to a ceramicbarrier, thereby protecting enclosed or separated areas. When partiallysubjected to fire, it may be desirable for the portion of the materialsubjected to the fire to transform to ceramic, being held in place bythe surrounding material that has not transformed to ceramic.Applications in the transport area may include panelling (eg in glassfibre reinforced thermoplastic or thermoset composites), exhaust,engine, braking, steering, safety devices, air conditioning, fuelstorage, housings and many others. Applications in defence would includeboth mobile and non-mobile weapons, vehicles, equipment, structures andother areas. Applications in the machinery area may include bearings,housing barriers and many others.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a cable having an insulating layer inaccordance with the invention; and

FIG. 2 is a perspective view of a multiconductor cable in whichcompositions of the invention are used as a sheath.

The compositions of the present invention are especially useful in thecoating of conductors. The compositions are therefore suitable for themanufacture of electrical cables that can provide circuit integrity inthe case of fire.

FIGS. 1 and 2 show single and multiconductor cables 1, 10 respectivelywhich have an insulation layer 2, or layers 12 and have a sheathinglayer 4, 14. In both of these cable designs, the insulation layer and/orthe sheathing layer are formed compositions in accordance with theinvention.

In the design of such cables the compositions can be used as an extrudedinsulation directly over conductors and/or used as an extruded sheathinglayer over an insulation layer or layers. Alternatively, they can beused as an interstice filler in multi-core cables, as individualextruded fillers added to an assembly to round off the assembly, as aninner layer prior to the application of wire or tape armour.

In practice the composition will typically be extruded onto the surfaceof a conductor. This extrusion may be carried out in a conventionalmanner using conventional equipment. The thickness of the layer ofinsulation will depend upon the requirements of the particular standardfor the size of conductor and operating voltage. Typically theinsulation will have a thickness from 0.6 to 3 mm. For example, for a 35mm² conductor rated at 0.6/1 kV to Australian Standards would require aninsulation thickness of approximately 1.2 mm. As noted, compositions inaccordance with the invention may exhibit excellent thermal andelectrical insulating properties at elevated temperature. When used suchcompositions enable a cable of elegantly simple design to bemanufactured since there is then no need to include a distinct layer toconfer electrical insulating properties. According to this aspect thepresent invention provides electrical cables consisting of a suitablecomposition in accordance with the present invention provided directlyon a conductor. The cable may include other layers such as acut-resistant layer and/or sheathing layer. However, the cable does notrequire an additional layer intended to maintain electrical insulationat elevated temperature.

EXAMPLES

The specification and claims refer to terms which are defined belowalong with test methods for their determination. The tests to determinethese properties should ideally be conducted on specimens 30 mm×13 mm×2mm (approximately), although in some examples specimens with somewhatdifferent dimensions have been used. The properties and conditions are:

-   -   Slow firing conditions. Heating test specimens from room        temperature to 1000° C. at a temperature increase rate of 12°        C./min followed by holding at 1000° C. for 30 minutes. These        conditions are those representative of ‘exposure to an elevated        temperature experienced under fire conditions.’    -   Fast firing conditions. Placing test specimens into a pre-heated        furnace at 1000° C. and maintaining the furnace at that        temperature for 30 minutes.

These conditions are representative of exposures that may be achievedunder a scenario of very rapid heating in a fire. In the examples, someof the compositions have been exposed to these firing conditions toillustrate the effect of different firing conditions on some of themeasured properties.

-   -   Change in linear dimension. The change in linear dimension along        the length of the specimen. The method of determining the change        in linear dimension is by measuring the length of the specimen        before firing and upon cooling after being subjected to slow        firing conditions. An expansion of specimen caused by firing is        reported as a positive change in linear dimension and a        contraction (shrinkage) as a negative change in linear        dimension. It is quoted as a percentage change. In the examples,        the change in linear dimension has also been determined on        samples that have been subjected to fast firing conditions to        compare the effects caused by different heating rates.    -   Flexural strength. The flexural strength of the ceramic is        determined by heating the test specimen under slow firing        conditions and, upon cooling, carrying out the determination by        three-point bending of a span length of 18 mm using a loading        cross head speed of 0.2 mm/minute. In the examples, flexural        strengths have also been determined on samples that have been        subjected to fast firing conditions to compare the effects        caused by different heating rates.    -   Residue. The material remaining after a composition has been        subjected to elevated temperatures experienced under fire        conditions. In the context of this invention, those conditions        are simulated heating the composition from room temperature to        1000° C. at a temperature increase rate of 12° C./min followed        by holding at 1000° C. for 30 minutes. Self supporting.        Compositions that remain rigid and do not undergo heat induced        deformation or flow. Determined by placing a specimen on a        rectangular piece of refractory so that the long axis is        perpendicular to the edge of the refectory block and a 13 mm        portion is projecting out from the edge of the block, then        heating under slow firing conditions and examining the cooled        specimen. A self supporting composition remains rigid, and is        able to support its own weight without bending over the edge of        the support. In the examples, the effect of varying the maximum        heating temperature is also shown.    -   Net shape retention. Compositions that undergo no substantial        change in shape when heated. This will depend in part on the        shape and dimensions of the specimen being tested and the firing        conditions used.    -   A two-roll mill was used to prepare the compositions described        in Examples 1, 2, 3, 4, 6, 7, 8 and 9. The ethylene propylene        rubber was banded on the mill (10-20° C.) and other components        were added and allowed to disperse by separating and recombining        the band of material just before it passed through the nip of        the two rolls. When these were uniformly dispersed, the peroxide        was added and dispersed in a similar manner.

Unless mentioned otherwise in an example, the following conditions wereused for specimen preparation:

-   -   Flat rectangular sheet specimens of required dimensions were        fabricated from the milled compositions containing        rubbers/elastomers by curing and moulding at 170° C. for 30        minutes under a pressure of approximately 7 MPa.

The fluxing oxide weight contributed to the residue after 100 g of eachof the clay, talc and mica used in the examples was heated at 1000° C.for 30 minutes was 1.0 g, 1.7 g and 11.1 g respectively. The residuecontent of each was 86.1 g, 96.0 g, and 96.9 g respectively. Unlessmentioned otherwise in an example, the average particle size of mica,clay and talc used in the examples was 160 μm, 1.5 μm and less than 10μm respectively.

Example 1

A number of compositions (see Table 1) were prepared and are denotedA-T. After firing, each sample took the form of a ceramic char. Thechange in linear dimension resulting from firing and the flexuralstrength of the ceramic char formed were determined as described aboveafter cooling the samples to room temperature. All of the samples shownin Table 1 are suitable for use as an insulation layer and/or sheathinglayer on a cable.

Composition A is an example of a basic composition that consists of onlyone organic polymer, silicate mineral fillers, a small amount of afluxing oxide and some additives.

Sample B is a composition comprising a blend of an organic polymer witha small amount of a silicone polymer which is a source of silica forchar formation. This composition does not contain any separately addedfluxing oxides (all the fluxes are derived from mineral fillers).

Sample C has a composition that contains a small amount of glass frit asa source of fluxing oxide. Comparison of Samples B and C shows that theaddition of a small amount of a glass as a source of fluxing oxide canimprove char strength.

Comparison of Samples C and D shows that some silicate mineral fillers,in this case clay, can lead to much higher char shrinkage than otherfillers.

Comparison of Samples D and E shows that adding higher amounts of glassfrit results in increased shrinkage and char strength.

Comparison of Samples F and G shows that removing volatile decompositionproducts from fillers such as clay by pre-calcining, reduces the charshrinkage with no significant adverse effect on char strength.

Comparison of Samples G and H shows that more talc and less clay isfavourable for reducing the char shrinkage.

Comparison of Samples A and H shows that the effect of boric oxide isindependent of the type of source used (zinc borate or boric oxide)provided the quantity of boric oxide is the same. This also shows thatzinc oxide introduced by zinc borate has no noticeable role in charshrinkage or strength. Its effect is similar to that of aluminium oxide.

Comparison of Samples J and K shows that higher amounts of boric oxideresults in higher amounts of shrinkage.

Sample M contains aluminium hydroxide and silicate mineral fillers withno separately added fluxing oxide.

Sample N is an example of a composition that does not contain any clayor talc, but contains aluminium hydroxide, mica and wollastonite.

Comparison of Samples O and P shows that larger particles of a mineralfiller reduce shrinkage.

Comparison of Samples Q, R and S shows that addition of fine silicaeither as silica powder or as a silicone polymer that decomposes givingsilica powder causes an increase in shrinkage and strength of char.TABLE 1 Composition A B C D E F G H J K Ethylene propylene rubber 2222.4 22 22 22 22 22 22 22 22 Silicone rubber 5.8 6 6 6 Clay 10 24 21 3010 10 10 Calcined clay 30.0 Talc 44 31.0 28 14 14 23 23 43 52 49Muscovite Mica 9 29.1 30 20 20 9 9 9 Zinc Borate 4 4 4 4 7 Glass Frit(flux content - 5.1%) 2 2 5 Fine silica Boric Oxide 1.35 Alumina 1.65Coarse Wollastonite Fine Wollastonite Aluminium tri-hydrate Peroxide 32.3 3 3 3 3 3 3 3 3 Other additives (lubricants, plasticisers, 9 9.4 9 99 9 9 9 9 9 antioxidents etc) Total 100 100 100 100 100 100 100 100 100100 Firing Condition Slow Slow Slow Fast Fast Fast Fast Slow Slow SlowLinear dimension change - % 3.8 0.5 1.2 6.1 8.8 5.4 7.0 3.4 3.3 6.3Flexural strength of char - MPa 8.2 1.1 2.6 3.1 9.4 5.2 5.3 7.4 7.4 7.6Total Flux - % 3.2 3.8 3.9 2.8 2.9 3.2 3.1 3.3 2.4 3.5 Total silicatemineral fillers - % 63.0 60.1 58.0 58.0 55.0 62.0 62.0 62.0 62.0 59.0Residue content after burning at 1000° C. - % 62.5 60.8 60.8 58.4 58.864.0 59.9 61.8 61.7 61.3 Flux content as a % at residue content 5.1 6.26.43 4.8 4.98 4.98 5.25 5.31 3.96 5.67 Composition L M N O P Q R S TEthylene propylene rubber 22 20 22 22 22 22 22 23.4 22 Silicone rubber4.8 6 6 6 1 5 6 Clay 19.2 14 14 24 24 25.5 24 Calcined clay Talc 64 1214 14 14 14 14.9 14 Muscovite Mica 16 20 20 20 20 20 21.3 20 Zinc Borate2 Glass Frit (flux content - 5.1%) 2 2 2 2 2 2.1 2 Fine silica 5 1 BoricOxide Alumina Coarse Wollastonite 10 Fine Wollastonite 18 10 Aluminiumtri-hydrate 20 20 Peroxide 3 2.4 3 3 3 3 3 3.2 3 Other additives(lubricants, plasticisers, 9 5.6 9 9 9 9 9 9.6 9 antioxidents etc) Total100 100 100 100 100 100 100 100 100 Firing Condition Slow Fast Fast SlowSlow Fast Fast Fast Fast Linear dimension change - % 2.0 3.1 0.0 3.9 4.86.0 5.7 3.2 6.8 Flexural strength of char - MPa 1.6 1.0 1.4 1.3 2.7 2.33.6 1.6 3.9 Total Flux - % 1.8 2.2 2.5 2.8 2.8 2.8 2.8 3.0 2.8 Totalsilicate mineral fillers - % 64.0 47.2 38.0 58.0 58.0 58.0 58.0 61.758.0 Residue content after burning at 1000° C. - % 63.0 58.9 55.3 59.759.7 61.0 58.9 59.0 58.4 Flux content as a % at residue content 2.91 3.74.46 4.66 4.66 4.6 4.76 5.1 4.8

Example 2

Electric cables were made using compositions B and T from the tableabove. Those made with composition T exhibited a high char shrinkagethat resulted in cracking of the insulation layer at 1050° C., leadingto insulation failure in the fire test (heating stage) according toAS/NZS 3013:1995. Cables made with the composition B that has a low charshrinkage passed the same test. The char produced was free of largevisible cracks in the case of composition B whereas the char formed fromcomposition T was heavily cracked leaving the conductor exposed.

Example 3

A composition (X) having the constituents listed in Table 2 below wasprepared. Composition X was based on a commercially available ethylenepropylene elastomer and silicone elastomer. The mica used was muscovitewith a mean particle size of 160 μm determined by sieve analysis. Glassfrit A has a softening point of 430° C. and a fluxing oxide content of30.8%. Glass frit B has a softening point of 600° C. and a fluxing oxidecontent of 5.1%. Glass fibers A, B and C have softening points of 580°C., 650° C. and 532° C., respectively and fluxing oxide contents of12-15%. Di(t-butylperoxyisopropyl) benzene peroxide was included in thecompositions for effecting thermal crosslinking. All compositions listedin this example are given in % wt/wt. TABLE 2 Components (% wt/wt)Ethylene propylene rubber 27 Silicone polymer 8 Muscovite mica 20 Glassfrit B 2 Clay 28 Talc 10 Zinc oxide 2 Peroxide 2 Antioxidants, coagents1 Total 100 Total Flux (%) 2.8 Fluxing oxide as a percent of residue 4.6

Example 3.1

Specimens of Composition X for strength testing were made withdimensions 50 mm×14 mm×3 mm and thermally crosslinked. For comparison,test specimens were similarly prepared using a commercially availablesilicone-based material (Composition Y), which also formed a ceramicmaterial when heated. The samples were heated together under slow firingconditions and then cooled. The flexural strength of ceramic formed andchange in linear dimension, determined as described above, are shown inTable 3. TABLE 3 Change in Linear Compositions Flexural Strength (MPa)Dimensions (%) Composition X 5.9 −1.6 Composition Y 4.2 −4.9

The results obtained from flexural strength measurements show thatComposition X has a higher flexural strength than the silicone-basedcomposition (Y) after firing in air at 1000° C.

Shape retention is a critical factor in many applications for thesetypes of materials, for example in electrical cable insulation.Measurements of change in linear dimension after firing at 1000° C. inair showed that Composition X had superior shape retention properties incomparison to Composition Y.

Example 3.2

A 35 mm² compacted copper conductor was insulated with 1.2 mm wallthickness of Composition X by an extrusion process. The insulatedconductor was then sheathed with a thermoplastic flame retardant halogenfree material to a wall thickness of 1.4 mm. Three samples of the cable,approximately 2.5 metres long, were installed on a ladder type cabletray in an “S” configuration with bend ratios of 10 times the cablediameter. The tray was mounted on a concrete slab and used to form thetop of a pilot furnace capable of following the standardtemperature-time curve of the Australian Standard AS1540.3. Each samplecable was connected to a three phase electrical supply such that thecables were on different phases. In each circuit was a 60W light bulband a 4A fuse. The line voltage was 240V AC. The test was started andcontinued for 121 minutes, at which time the temperature in the furnacewas approximately 1,050° C. At the completion of this time, the circuitintegrity of all of the samples was maintained. A water jet spray wasthen trained on the cables and circuit integrity continued to bemaintained.

Example 3.3

Composition X was modified by adding small amounts of various inorganicadditives in the proportions outlined in the table below. The inorganicadditives included glass fibre, glass frit and alumino-silicate fibre.Composition X and the modified versions were thermally crosslinked (170°C., 30 minutes, 7 MPa) into flat sheets 2 mm thick. Rectangular samplesof dimensions 19 mm×32 mm were cut out of the sheets and subjected toslow firing conditions. After cooling, the samples were tested for waterresistance by placing a drop of water on the sample surface. Thematerial was deemed to be water resistant if a drop of water remained onthe sample surface for more than three minutes without any visual signof absorption. The material was not considered water resistant if thewater drop was completely absorbed in less than three minutes. Theresults of this test are shown in Table 4. TABLE 4 Water CompositionResistant Composition X No Composition X/Glass fibre A (98:2) YesComposition X/Glass fibre A/alumino-silicate fibre (96:2:2) YesComposition X/Glass fibre B (98:2) Yes Composition X/Glass frit A (98:2)Yes Composition X/Glass frit A/alumino-silicate fibre (96:2:2) Yes

A water drop placed on a fired sample of unmodified Composition X wasabsorbed instantly. From visual inspection the fired samples of othercompositions containing the inorganic additives had a glassy, shinysurface layer.

Example 3.4

Six samples corresponding to the six compositions in the previousexample were sectioned such that their thickness was reduced from 2 mmto 1 mm. Samples were then subjected to slow firing conditions. Aftercooling they were tested for water resistance in the same mannerdescribed in the preceding example. In all six cases the samplesabsorbed a drop of water placed on their surface in less than oneminute, indicating a lack of water resistance. A comparison with theresults in the previous example shows that sample thickness is a factorin developing water resistance.

Example 3.5

(A)

Sections of 1.5 mm² copper wire were insulated with Composition X andmodifications to this composition as outlined in Tables 5 and 6. Thewall thicknesses were set at 1.2 mm and 0.6 mm to obtain cables withthick and thin insulation layers. Insulated cables were put together toform twisted pairs. Each twisted pair was exposed to a Bunsen burnerflame for 10 minutes. The burner and cable were configured so that thepeak temperature at the flame-sample interface was measured at 1020° C.The cable was allowed to cool and water was dripped across the portionof the twisted pair to assess the time taken for the circuit to short.During the burner and water test the resistance between the two wires inthe twisted pair was monitored using a 500 V DC test unit. Failure ineither test was deemed to be the measured resistance dropping toapproximately 0 MΩ at any point in the test. The compositions and theirperformance in the tests for thick insulation layers are shown in Table5 and for thin insulation layers are shown in Table 6 TABLE 5 BurnerWater Test Test (time Composition (pass/fail) to short) Composition XPass <30 seconds Composition X/alumino-silicate fibre Pass >3 minutes(99:1) Composition X/Glass frit A (99:1) Pass >3 minutes CompositionX/alumino-silicate fibre/Glass Pass >3 minutes frit A (99:0.5:0.5)

The results in Table 5 showed that additions of glass frit and/oralumino-silicate fibre in amounts totalling no more than 1% wt/wtimparted good water resistance properties to Composition X. CompositionX, without any additions, had almost negligible water resistance, with ashort circuit occurring in less than 30 seconds after water contactedthe cable. TABLE 6 Water Burner Test Test (time to Composition(pass/fail) short) Composition X Pass <30 seconds CompositionX/alumino-silicate fibre/Glass Pass <30 seconds frit A (98.5:0.5:1)Composition X/alumino-silicate fibre/Glass Pass <1 minute fibre A(97:1:2) Composition X/alumino-silicate fibre/Glass Pass <30 secondsfibre A (96:1:3) Composition X/alumino-silicate fibre/Glass Pass <30seconds fibre A/Glass frit A (94:1:3:2) Composition X/alumino-silicatefibre/Glass Pass <30 seconds fibre C (94:1:5)

The results in Table 6 showed that when a change from 1.2 mm to 0.6 mmwall thicknesses was made, no tested composition exhibited acceptablewater resistance. Again, this demonstrates that the thickness of thesample is a factor in developing water resistance.

(B)

In order to improve the water resistance of thin wall (0.6 mm) cables,an addition of alumino silicate fibre and mica were made to CompositionX to give a new composition consisting of Composition X/alumino silicatefibre/mica (94:1:5). The fluxing oxide content of the residue obtainedunder slow firing conditions was 5.1%. The composition was formed intothin wall twisted pair cables and tested in the burner according to theprocedure described in the previous example. The wire passed the burnertest and the time to short in the water test was greater than 3 minutes.

Example 3.6

Fired 2 mm thick samples of Composition X modified with inorganicadditives to improve water resistance were analysed by scanning electronmicroscopy and microprobe analysis in order to assess the reason fortheir water resistance. Micrographs of the sample cross-section showedthat a dense glassy layer ranging up to 15 μm in thickness was presentat the surface. This glassy film 20 overlays the porous bulk of thematerial, protecting it from water absorption. Microprobe mappinganalysis of a cross-section of the sample showed that this dense glassylayer is rich in potassium, sodium and silica.

Example 4

A composition with an EPDM polymer (20%), talc (30%), muscovite mica(29%) and processing aids and stabilisers was prepared on a two rollmill. At the completion of mixing, it was separated into two equalportions. One portion was returned to the two roll mill, and 2% ofdicumyl peroxide was added. The two portions were then placed separatelyinto picture frame moulds and pressed at 1,000 kPa and 170° C. for 30minutes. At the end of this period, the press was cooled whilemaintaining pressure, and after the temperature had reduced to 50° C.,the pressure was reduced and the samples removed. The end result was twosheets of material that had undergone the same heat history, but one hadbeen crosslinked while the other was thermoplastic.

Samples of dimensions 38 mm×13 mm were cut from the sheets, and thedimensions accurately recorded. The samples were subjected to slowfiring conditions and then the samples were removed from the furnace andallowed to cool to ambient temperature. The dimensions of the ceramicresidue formed (fluxing oxide content 6.6%) were then accuratelyre-measured and the change in linear dimension calculated.

It was found that the thermoplastic version showed less surfacedisruption than the crosslinked version, expanded less in thickness, butslightly more in length and width. This illustrates that crosslinking ofthe composition is not essential to achieving an acceptable performancein net shape retention after exposure to 1,000° C.

Example 5

Compositions based on a representative range of different polymerscombined with inorganic filler systems selected from Table 7 wereprepared and their behaviour when fired under fast or slow firingconditions was determined. TABLE 7 Filler system A B C D E F Clay 31.716.2 Clay (calcined) 15.2 25.4 14.7 21.5 17.5 Talc 36.2 35 32.9 34.938.4 Muscovite mica 45.5 39.7 44 38.7 41.5 43.1 Zinc borate 3.1 3 6.96.1 Glass frit 3.2 3.3 2.3

Some different ways of making compositions disclosed in this patent areexemplified below.

(A) From Monomers/Reactive Difunctional Compounds

(i)

A composition containing filler system A (58.9%) and an acrylic polymerwas prepared by mixing the inorganic components with a mixture ofacrylate monomers and peroxide then heating the mixture in a mould at80° C. for 2 hours. The ceramic formed (fluxing oxide content 7.2%)under the fast firing conditions had a linear dimension change of 0.9%and a flexural strength of 0.5 MPa.

(ii)

A composition containing filler system E (62.2%) and a polyimide wasprepared by partly reacting equimolar amounts of pyromelliticdianhydride with oxydianaline bis(4-aminophenyl)ether polymer, addingthe filler system and then heating the cast solutions for one hourperiods at 100° C., 150° C., 200° C. and then 250° C. The ceramic formed(fluxing oxide content 7.9%) under the fast firing conditions had lineardimension change 3.4% and a flexural strength of 5.3 MPa.

(B) From Thermoplastic Polymers and Rubbers

The compositions in Table 8 were prepared by incorporating the indicatedfiller systems into the thermoplastic polymer (combined with otheradditives where indicated) using an internal mixer, an extruder or atwo-roll mill. The compositions containing SBR, SBS and NBR alsoincorporated peroxides and were subsequently cured by heating atelevated temperatures to form elastomeric compositions which weresubsequently fired. TABLE 8 Percent Percent fluxing Percent other FillerFiring oxide linear Flexural Polymer addi- system con- content ofdimension strength (%) tives (%) ditions residue change (MPa) PE(25)^(b) 4.7 B (63) Fast 5.2 −2.3 1.7 Slow −1.6 1.4 PP (38) 2 C (60)Fast 8 1.4 0.4 Slow 2.2 0.6 EVA (38) 2 C (60) Slow 8 0.9 0.7 EMA (40) —C (60) Fast 8 4.5 1.3 Slow −3.4 0.8 SBS (30) 12 A (58) Fast 7.2 −3.2 3Slow −2.7 3.5 SBR (30) 12 A (58) Fast 7.2 1.2 2.8 Slow −2.4 1 NBR (30)12 A (58) Fast 7.2 −1.2 1.3 Slow −0.8 3.8 PVC (20) (15.0) F (65) Slow(9.1) (−2.6) 8.3^(b)In addition the composition contains 7.3% silicone polymer(C) From Prepolymers and Resins

The thermoset compositions in Table 9 were prepared by incorporating theindicated filler systems into the prepolymers or resins and the systemswere crosslinked/cured using the conditions indicated. TABLE 9 Percentfluxing Crosslinking/ oxide Percent curing Filler content linearFlexural agent system Firing of dimension strength Prepolymer/resin (%)(conditions) (%) conditions residue change (MPa) Epoxy resin with amine(40° C./3 h A (59.5) Fast 7.2 0.8 1.4 hardner (40.5) and Slow −0.7 2.180° C./1 h) Vinyl ester resin (40) Peroxide A (60) Fast 7.2 −1 1.8 (80°C./2 h) Slow −1 2.7 Polyester resin (44.4) Peroxide A (55.6) Slow 7.2−3.6 1.5 (80° C./2 h) Phenolic resin (44.2)*** (140° C./1 h) A (55.8)Fast 7.2 −3.9 3.6 Slow −2.6 5.2 Flexible Foamed (25° C./3 h) A (60) Fast7.2 −0.5 0.9 Polyurethane (40) Slow −2.6 1 Cast Polyurethane (40) (25°C./3 h) A (60) Fast 7.2 0.4 3.6 Slow −0.1 1.2***Among the best examples for near-net shape retaining compositions.(D) From Polymer Emulsions/Dispersions

The compositions in Table 10 were prepared by incorporating theindicated filler systems into the emulsions/dispersions and drying theresulting mixture (typically 3 days at 70° C.) to remove the water. Thepercentage polymer in the compositions is the weight of dry polymerpresent. TABLE 10 Percent Polymer fluxing from oxide Percent emulsion/Filler content linear Flexural dispersion system Firing of dimensionstrength (%) (%) conditions residue change (MPa) PVAc D (70) Fast 7.9−2.5 2.4 emulsion (30) Slow −2.1 5.5 Acrylic C (80) Fast 8 0.3 3.5dispersion (20) Slow 0.5 5.4 Polyurethane C (60) Fast 6.7 1.8 0.4dispersion (40) Slow 2.1 0.7

Example 6

Compositions Y1 to Y11, given in Table 11, contain ethylene propylenerubber or a combination of ethylene propylene rubber and siliconepolymer where the silicone polymer is in the minor amount. These wereprepared by mixing the polymer(s) with the respective filler andadditive combination using a two roll mill as described earlier.Specimens of nominal dimensions 30 mm×13 mm×1.7 mm, made from thesecompositions, were fired under the slow and fast firing conditions. Foreach composition, the change in linear dimension caused by firing andthe flexural strength of the resultant ceramic, determined as describedearlier, are given in Table 11. TABLE 11 Percent Flexural fluxingPercent strength Percent Percent Percent oxide linear of ethylenePercent other Percent other content dimension ceramic propylene siliconeorganic silicate inorganic Firing of change formed Composition rubberpolymer additives fillers fillers condition residue on firing (MPa) Y1*22.0 12.0 64.0 2.0 Fast 7.2 −3.1 2.9 Slow −4.2 9.7 Y2*{circumflex over( )}{circumflex over ( )}{circumflex over ( )} 22.0 12.0 64.0 2.0 Fast7.2 −2.7 5.8 Slow −0.9 7.4 Y3 30.0 12.0 56.2 1.8 Fast 7.2 −2.5 2.4 Slow0.5 4.3 Y4 42.0 12.0 44.6 1.4 Fast 7.2 −2.1 0.3 Slow ** Y5 32.0 10.0 6.043.2 8.8 Fast 7.2 −3.4 4.3 Slow ** Y6^(##) 13.0 12.0 72.7 2.3 Fast 7.2−2.7 13.9 Slow −2.8 20.4 Y7 27.0 13.0 12.0 24.0 24.0 Fast 4.2 −4.5 1Slow ** Y8 22.0 11.0 6.0 45.0 16.0 Fast 6.6 −9.3 7 Slow −9 9.9Y9{circumflex over ( )}{circumflex over ( )}{circumflex over ( )} 22.04.0 12.0 60.0 2.0 Fast 7.3 −1.8 3.1 Slow −0.8 1.8 Y10 22.0 12.0 62.0 4.0Fast 9.5 −3.5 5.7 Slow −6.2 13.5 Y11 22.0 12.0 66.0 Fast 1.6 0.8 2.1Slow ***These compositions were chemically identical. The average particle sizeof major mineral filler in composition Y1 was approximately 55 micronswhile the average particle size of major mineral filler in compositionY2 was approximately 160 microns.** Could not test for dimensional change and strength due to non-uniformdeformation during firing.^(##)Processability using two-roll mill was poor.{circumflex over ( )}{circumflex over ( )}{circumflex over ( )}Among thebest examples for near-net shape retaining compositions

Example 7

Composition FL, given in Table 12, were prepared by mixing the ethylenepropylene rubber with the respective filler and additive combinationusing a two roll mill as described earlier. Compositions FL1 to FL4,given in Table 12, were prepared by adding. 2% of a fluxing oxide tocomposition FL and mixing again. Specimens of nominal dimensions 30mm×13 mm×1.7 mm, made from these compositions were fired under the slowand fast firing conditions. For each composition, the change in lineardimension caused by firing and the flexural strength of the resultantceramic, determined as described earlier, are given in Tables 12. TABLE12 Percent flexural fluxing Percent strength Percent Percent Added oxidelinear of ethylene other Percent fluxing content dimension ceramicpropylene organic silicate oxide⁺⁺ Firing of change on formedComposition rubber additives fillers (%) condition residue firing (MPa)FL 22.5 12.2 65.3 — Fast 3.4 −0.7 1.1 Slow −0.8 1.4 FL1 22.0 12.0 64.0Li₂O (2) Fast 6.4 −4.0 6.1 Slow −3.5 5.4 FL2 Na₂O (2) Fast −2.3 2.6 Slow−1.9 6.0 FL3 K₂O (2) Fast 0.1 1.9 Slow −0.4 3.2 FL4 B₂O₃ (2) Fast −2.72.8 Slow −3.8 2.8⁺⁺Added as oxide or carbonate in an amount that produces 2% oxide bythermal decomposition.

Example 8

Compositions FX1 to FX3, given in Table 13, were prepared by mixing theethylene propylene rubber with the respective filler and additivecombination using a two roll mill as described earlier. FX1 is acomposition in accordance with the specifications for the fire resistantmaterial of the present invention. FX2 and FX3 are comparative examplecompositions containing higher amounts of fluxing oxides and loweramounts of silicate mineral fillers than recommended for the fireresistant material of the present invention. Specimens of nominaldimensions 30 mm×13 mm×1.7 mm, made from these compositions, were placedon a rectangular piece of refractory so that their long axis wasperpendicular to one edge of the supporting refractory block and a 13 mmlong portion of each specimen was projecting out from the edge of thesupporting refractory block.

They were then heated at 12° C. per minute to 830° C. and 1000° C. andmaintained at these temperatures for 30 minutes in air. At bothtemperatures, the specimens of composition FX1 did not fuse and produceda coherent self-supporting porous ceramic that retained the shape of thespecimen prior to exposure to elevated temperatures. The change indimension of the specimens of composition FX1 along the length and thewidth was less than 3%. At both temperatures, the specimens ofcompositions FX2 and FX3 fused and the unsupported span bent over theedge of the refractory support to take a near vertical position showingtheir inability to retain shape or support own weight. When heated to1100° C. the specimens of compositions FX2 and FX3 fused completely toform a glassy material that flowed on and along the sides of therefractory support whereas the specimens of composition FX1 remainedrigid. TABLE 13 Percent Percent Percent Percent ethylene other Percentother fluxing Compo- propylene organic silicate inorganic oxide contentsition rubber additives fillers fillers of residue FX1 22.0 12.0 64.02.0 72 FX2 22.7 15.0 18.2 44.0 65.6 FX3 22.2 14.0 17.8 46.0 77.0

Example 9

Compositions OF1 to OF6, given in Table 14, were prepared by mixing theethylene propylene rubber with the respective filler and additivecombination using a two roll mill as described earlier. Composition OF7,given in Table 14, was prepared by adding 4% of alumina fibres tocomposition OF6 and mixing again. Specimens of nominal dimensions 30mm×13 mm×1.7 mm, made from these compositions were fired under the slowor fast firing conditions. For each composition, the change in lineardimension caused by firing and the flexural strength of the resultantceramic, determined as described earlier, are given in Table 14. Of thesamples shown in Table 14, OF1 and OF2 are most suitable for use as aninsulating layer and/or sheathing layer on a cable. TABLE 14 PercentFlexural fluxing Percent strength Percent Percent oxide linear ofethylene other Percent Percent Other content dimension ceramic propyleneorganic silicone silicate inorganic Firing of change on formedComposition rubber additives polymer fillers fillers (%) conditionresidue firing (MPa) OF1 19.0 16.0 5.0 40.0 ATH* Fast 4.7 −0.3 1.1 (10),CaCO₃ (10) OF2 19.0 16.0 6.0 30.0 ATH* Fast 4.7 −3.9 2.2 (29) OF3 22.012.0 64.0 BaO (2) Fast 3.3 −1.1 1.9 Slow −1.3 2.6 OF4 CaO (2) Fast −1.61.5 Slow −1.5 1.9 OF5 Fe₂O₃ (2) Fast −1.0 1.4 Slow −1.3 1.1 OF6 25.0 4.07.0 61.0 3.0 Slow 5.3 −2.4 5.2 OF7 24.0 3.8 6.7 58.6 6.9^(##) Slow 5.0−1.6 5.8*Aluminium tri-hydrate^(##)Includes 4% alumina fibres

Throughout this specification and the claims which follow, unless thecontext requires otherwise, the word “comprise”, and variations such as“comprises” and “comprising”, will be understood to imply the inclusionof a stated integer or step or group of integers or steps but not theexclusion of any other integer or step or group of integers or steps.

1. A fire resistant composition for forming a fire resistant ceramic atelevated temperatures, the composition comprising: at least 15% byweight based on the total weight of the composition of a polymer basecomposition comprising at least 50% by weight of an organic polymer; atleast 15% by weight based on the total weight of the composition of asilicate mineral filler; and at least one source of fluxing oxide whichis optionally present in said silicate mineral filler, wherein afterexposure to an elevated temperature experienced under fire conditions, afluxing oxide is present in an amount of from 1 to 15% by weight of theresidue.
 2. The fire resistant composition of claim 1, wherein thesilicate mineral filler is present in an amount of at least 25% byweight based on the total weight of the composition.
 3. The fireresistant composition of claim 1, wherein the fluxing oxide is presentin the residue in an amount of 1-10 wt. % after exposure to saidelevated temperatures.
 4. The fire resistant composition of claim 1,wherein the fluxing oxide is present in the residue in an amount of 2-8wt. % of the residue after exposure to said elevated temperature.
 5. Thefire resistant composition of claim 1, wherein the weight of the residueafter firing is at least 40% of the fire resistant composition.
 6. Afire resistant composition of claim 1, wherein the composition forms aself-supporting structure when heated to an elevated temperatureexperienced under fire conditions.
 7. The fire resistant composition ofclaim 1, wherein the fluxing oxide is generated by the silicate mineralfiller being heated to an elevated temperature.
 8. The fire resistantcomposition of claim 1, wherein the fire resistant composition furthercomprises at least one additive selected from the group of a fluxingoxide and precursors of fluxing oxides.
 9. The fire resistantcomposition of claim 8, wherein the composition comprises at least twodifferent fluxing oxides or precursors to fluxing oxides which formliquid phases at different temperatures.
 10. A fire resistantcomposition according to claim 8, wherein the at least one of fluxingoxide precursor comprises one or more materials selected from the groupconsisting of borates, metal hydroxides, metal carbonates and glasses.11. A fire resistant composition according to claim 8, wherein thefluxing oxide added or derived from precursors comprises at least oneoxide of an element selected from the group consisting of lead,antimony, boron, lithium, potassium, sodium, phosphorous and vanadium.12. A fire resistant composition according to claim 1, wherein thecomposition has less than 10% change in linear dimension after heatingat an elevated temperature experienced under fire conditions.
 13. A fireresistant composition according to claim 1, wherein the composition hasless than 5% change in linear dimension after heating at an elevatedtemperature experienced under fire conditions.
 14. A fire resistantcomposition according to claim 1, wherein the composition remainscoherent when heated to temperatures of less than 1050° C. for minutes.15. The fire resistant composition of claim 1, wherein after exposure toan elevated temperature experienced under fire conditions, the fireresistant composition has a flexural strength of at least 0.3 MPa.
 16. Afire resistant composition of claim 1, wherein the organic polymer isselected from the group of thermoplastic polymers, thermoset polymersand elastomers.
 17. A fire resistant composition of claim 1, wherein theorganic polymer comprises at least one of homopolymer or copolymer orelastomer or resin of polyolefins, ethylene-propylene rubber,ethylene-propylene terpolymer rubber (EPDM), chlorosulfonatedpolyethylene and chlorinate polyethylene, vinyl polymers, acrylic andmethacrylic polymers, polyamides, polyesters, polyimides,polyoxymethylene acetals, polycarbonates, polyurethanes, natural rubber,butyl rubber, nitrile-butadiene rubber, epichlorohydrin rubber,polychloroprene, styrene polymers, styrene-butadiene,styrene-isoprene-styrene,styrene-butadiene-styrene,styrene-ethylene-butadiene-styrene, epoxy resins, polyester resins,vinyl ester resins, phenolic resins, and melamine formaldehyde resins.18. The fire resistant composition of claim 1, wherein the polymer basecomposition comprises from 15 to 75 wt. % of the formulated fireresistant composition.
 19. The fire resistant composition of claim 1,wherein the silicate mineral filler is at least one selected from thegroup consisting of alumino-silicates, alkali alumino-silicates,magnesium silicates and calcium silicates.
 20. The fire resistantcomposition of claim 1, comprises an additional inorganic fillerselected from the group consisting of silicon dioxide and metal oxidesof aluminium, calcium, magnesium, zircon, zinc, iron, tin and barium andinorganic fillers which generate one or more of these oxides when theythermally decompose.
 21. The fire resistant composition of claim 1,wherein the polymer base composition further comprises a siliconepolymer.
 22. The fire resistant composition of claim 21, wherein theweight ratio of organic polymer to silicone polymer is within the rangeof 5:1 to 2:1.
 23. The fire resistant composition of claim 1, furthercomprising a silicone polymer in an amount of from 2 to 15 wt. % basedon the total weight of the formulated fire resistant composition.
 24. Afire resistant composition according to claim 1, wherein the 5 elevatedtemperature experienced under fire conditions is 1000° C. for 30minutes.
 25. A fire resistant composition according to claim 1, wherein:20 to 75% by weight of said polymer base composition wherein saidcomposition further comprises a silicone polymer; at least 15% by weightof an inorganic filler wherein said inorganic filler comprises mica anda glass additive; and wherein the fluxing oxide in the residue isderived from glass and mica wherein, the ratio of mica: glass is in therange of from 20:1 to 2:1.
 26. A fire resistant composition according toclaim 25, wherein the polymer base composition comprises organic polymerand silicone polymer in the weight ratio of from 5:1 to 2:1; saidinorganic filler comprises 10 to 30% by weight of the total compositionof mica and 20 to 40% by weight of the total composition of anadditional inorganic filler.
 27. A fire resistant composition of claim1, wherein the fluxing oxide is present in the residue in an amount inexcess of 5% by weight of the residue, said fluxing oxide forming aglassy surface layer on the ceramic formed on exposure to fire, saidglassy surface layer forming a barrier layer which increases theresistance to passage of water and gases.
 28. A fire resistant cablecomprising a conductive element and at least one insulating layer and/orsheathing layer made of a fire resistant composition for providing afire resistant ceramic under fire conditions, the fire resistantcomposition comprising: at least 15% by weight based on the total weightof the composition of a polymer base composition comprising at least 50%by weight of an organic polymer; at least 15% by weight based on thetotal weight of the composition of a silicate mineral filler; and atleast one source of fluxing oxide which is optionally present in saidsilicate mineral filler, wherein after exposure to an elevatedtemperature experienced under fire conditions, a fluxing oxide ispresent in an amount from 1 to 15% by weight of the residue.
 29. A fireresistant cable of claim 28, wherein the silicate mineral filler ispresent in an amount of at least 25% by weight based on the total weightof the composition.
 30. The fire resistant cable of claim 28, whereinthe fluxing oxide is present in the residue in the fire resistantcomposition in an amount of 1-10 wt. % after exposure to said elevatedtemperatures.
 31. The fire resistant cable of claim 28, wherein thefluxing oxide is present in the residue of the fire resistantcomposition in an amount of 2-8 wt. % after exposure to said elevatedtemperature.
 32. The fire resistant cable of claim 28, wherein theweight of the residue after firing is at least 40% of the fire resistantcomposition.
 33. A fire resistant cable of claim 28, wherein thecomposition forms a selfsupporting structure when heated to an elevatedtemperature experienced under fire conditions.
 34. The fire resistantcable of claim 28, wherein the fluxing oxide is generated by thesilicate mineral filler being heated to an elevated temperature.
 35. Thefire resistant cable of claim 28, wherein the fire resistant compositionfurther comprises at least one additive selected from the group offluxing oxides and precursors to fluxing oxides.
 36. The fire resistantcable of claim 35, wherein the fire resistant composition 5 comprises atleast two different fluxing oxides or precursors to fluxing oxides whichform liquid phases at different temperatures.
 37. A fire resistant cableaccording to claim 35, wherein at least one of fluxing oxide precursorcomprises one or more materials selected from the group consisting ofborates, metal hydroxides, metal carbonates and glasses.
 38. A fireresistant cable according to claim 35, wherein the fluxing oxide addedor derived from a precursor to a fluxing oxide comprises at least oneselected from the group consisting of an oxide of an element selectedfrom the group consisting of boron, lithium, potassium, sodium,phosphorous vanadium, lead and antimony.
 39. A fire resistant cableaccording to claim 28, wherein the composition has less than 10% changein linear dimension after heating at an elevated temperature experiencedunder fire conditions.
 40. A fire resistant cable of claim 28, whereinthe composition has less than 5% change in linear dimension afterheating at an elevated temperature experienced under fire conditions.41. A fire resistant cable according to claim 28, wherein the fireresistant composition remains coherent when heated to temperatures ofless than 1050° C. for 30 minutes.
 42. A fire resistant cable of claim28, wherein the organic polymer is a thermoplastic and crosslinkedolefin based polymer selected from the group of homopolymers of olefins,copolymers or terpolymers of one or more olefins and a blend ofhomopolymers, copolymers and terpolymers.
 43. A fire resistant cable ofclaim 28, wherein the organic polymer comprises at least one ofhomopolymer or copolymer or elastomer or resin of polyolefins,ethylene-propylene rubber, ethylene-propylene terpolymer rubber (EPDM),chlorosulfonated polyethylene and chlorinate polyethylene, vinylpolymers, acrylic and methacrylic polymers, polyamides, polyesters,polyimides, polyoxymethylene acetals, polycarbonates, polyurethanes,natural rubber, butyl rubber, nitrile-butadiene rubber, epichlorohydrinrubber, polychloroprene, styrene polymers, styrene-butadiene,styrene-isoprene-styrene,styrene-butadiene-styrene,styrene-ethylene-butadiene-styrene, epoxy resins, polyester resins,vinyl ester resins, phenolic resins, and melamine formaldehyde resins.44. A fire resistant cable of claim 28, wherein the fire resistantcomposition comprises an additional inorganic filler selected from thegroup consisting of silicon dioxide and metal oxides of aluminium,calcium, magnesium, zircon, zinc, iron, tin and barium and inorganicfillers which generate one or more of these oxides when they thermallydecompose.
 45. A fire resistant cable comprising a conductive elementand at least one insulating layer and/or sheathing layer made of a fireresistant composition of claim
 1. 46. A fire resistant cable of claim28, wherein the polymer base composition in the fire resistantcomposition further comprises a silicone polymer.
 47. A fire resistantproduct formed from the composition of claim
 1. 48. The fire resistantproduct of claim 47, used in passive fire protection applications andgeneral engineering applications where passive fire protectionproperties are required.